Imaging lens and imaging apparatus equipped with the imaging lens
View Patent ↗An imaging lens is constituted essentially by six lenses, including: a first lens having a positive refractive power and is of a meniscus shape with a convex surface toward the object side; a second lens having a negative refractive power; a third lens; a fourth lens having a positive refractive power; a fifth lens having a negative refractive power and a concave surface toward the image side; and a sixth lens of a biconcave shape, provided in this order from the object side. The imaging lens satisfies a predetermined conditional formula.
1. An imaging lens consisting essentially of six lenses, including:
a first lens having a positive refractive power and is of a meniscus shape with a convex surface toward the object side;
a second lens having a negative refractive power;
a third lens;
a fourth lens having a positive refractive power;
a fifth lens having a negative refractive power and a concave surface toward the image side; and
a sixth lens of a biconcave shape, provided in this order from the object side;
the imaging lens satisfying the following conditional formula:
−0.25< f/f 3<1 (1)
wherein f is the focal length of the entire system, and f3 is the focal length of the third lens, and
the imaging lens satisfying the following conditional formula:
1. 2 < f/f 4 <1.95 (5-2)
wherein f4 is the focal length of the fourth lens.
2. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−3.5< f/f 5<0 (2)
wherein f5 is the focal length of the fifth lens.
3. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−4< f 4/ f 5<0 (3)
wherein f4 is the focal length of the fourth lens, and f5 is the focal length of the fifth lens.
4. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−2< f/f 2<0 (4)
wherein f2 is the focal length of the second lens.
5. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
0.7< f/f 1<2 (6)
wherein f1 is the focal length of the first lens.
6. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−3< f·P 34<0 (7)
wherein P34 is the refractive power of an air gap formed between the surface of the third lens toward the image side and the surface of the fourth lens toward the object side, the refractive power of the air gap being obtained by Formula (P) below:
P
34
=
1
-
Nd
3
L
3
r
+
Nd
4
-
1
L
4
f
-
(
1
-
Nd
3
)
×
(
Nd
4
-
1
)
×
D
7
L
3
r
×
L
4
f
(
P
)
wherein Nd3 is the refractive index of the third lens with respect to the d line, Nd4 is the refractive index of the fourth lens with respect to the d line, L3r is the paraxial radius of curvature of the surface of the third lens toward the image side, L4f is the paraxial radius of curvature of the surface of the fourth lens toward the object side, and D7 is an air space distance between the third lens and the fourth lens along the optical axis.
7. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−10<( L 4 r+L 4 f )/( L 4 r−L 4 f )<4 (8)
wherein L4f is the paraxial radius of curvature of the surface of the fourth lens toward the object side, and L4r is the paraxial radius of curvature of the surface of the fourth lens toward the image side.
8. An imaging lens as defined in claim 1 , further comprising:
an aperture stop positioned at the object side of the surface of the first lens toward the object side.
9. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−0.24< f/f 3<0.8 (1-1).
10. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−2.5< f/f 5<0 (2-1)
wherein f5 is the focal length of the fifth lens.
11. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−2< f 4/ f 5<0 (3-1)
wherein f4 is the focal length of the fourth lens and f5 is the focal length of the fifth lens.
12. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−1< f/f 2<−0.3 (4-1)
wherein f2 is the focal length of the second lens.
13. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
0.81< f/f 1<1.5 (6-1)
wherein f1 is the focal length of the first lens.
14. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−1.5< f·P 34<−0.2 (7-1)
wherein P34 is the refractive power of an air gap formed between the surface of the third lens toward the image side and the surface of the fourth lens toward the object side, the refractive power of the air gap being obtained by Formula (P) below:
P
34
=
1
-
Nd
3
L
3
r
+
Nd
4
-
1
L
4
f
-
(
1
-
Nd
3
)
×
(
Nd
4
-
1
)
×
D
7
L
3
r
×
L
4
f
(
P
)
wherein Nd3 is the refractive index of the third lens with respect to the d line, Nd4 is the refractive index of the fourth lens with respect to the d line, L3r is the paraxial radius of curvature of the surface of the third lens toward the image side, L4f is the paraxial radius of curvature of the surface of the fourth lens toward the object side, and D7 is an air space distance between the third lens and the fourth lens along the optical axis.
15. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−5<( L 4 r+L 4 f )/( L 4 r−L 4 f )<0 (8-1)
wherein L4f is the paraxial radius of curvature of the surface of the fourth lens toward the object side, and L4r is the paraxial radius of curvature of the surface of the fourth lens toward the image side.
16. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
−0.23< f/f 3<0.46 (1-2).
17. An imaging apparatus equipped with an imaging lens as defined in claim 1 .